In the production of oriented film, for example, the film is transported through an oven that will heat and/or cool the film. A typical oven consists of slot nozzles which provide convective heat transfer by air impinging on the film, and mechanical means (such as a tenter) for transporting and stretching the film. The tenter consists of clips that clamp to the edge of the film and rails that guide the clips through the oven. The distance between rails is typically adjustable to allow for the production of different width films and different stretch rates.
In order to allow for the adjustment of the rails depending on the film width, the slot nozzles, which are arranged on either side of the plane of travel of the film, are positioned above and below the rails. As a result, nozzle-to-film distances are less than optimum, sometimes being as much as sixteen (16) inches apart. As the nozzle-to-film distance increases, the heat transfer coefficient and uniformity decreases, thereby resulting in an inefficient oven and poorer quality film.
In response to problems similar to the foregoing, U.S. Pat. Nos. 2,270,155 and 2,495,163 disclose the use of nozzles having variable lengths according to the width of a cloth being treated. The nozzles include a fixed part corresponding to the minimum width of the cloth to be treated, and extensions slidably mounted on the fixed part, which are responsive to the movements of the chain-guide rails. As a result, the nozzles need not be located above and below the top and bottom rails, respectively, but instead can be located in the same planes as the rails.
The present invention is directed to an improved telescoping slot nozzle for tenter frames as hereinafter described.